Gulf of Thailand large marine ecosystem

Introduction

Location of the Gulf of Thailand Large Marine Ecosystem (Source: NOAA)

The Gulf of Thailand Large Marine Ecosystem (LME) is a semi-enclosed sea located in Southeast Asia off of the South China Sea. Intensive fishing is the primary force driving the LME, with climate as the secondary driving force. Monsoon seasons and the intrusion of seawater from the South China Sea are causes of oceanographic change. The Gulf of Thailand is part of the Sunda Shelf and is relatively shallow, with depths varying between 45 and 80 meters (m). Twenty-three rivers, including 5 major ones, drain large amounts of fresh water into the Gulf. The countries bordering this LME are Thailand, Vietnam and Cambodia. LME book chapters and articles pertaining to this LME include Piyakarnchana, 1989; Pauly and Christensen, 1993; Piyakarnchana, 1999; and Pauly and Chuenpagdee, 2003.

Productivity

For a map of the LME’s features, see Pauly and Chuenpagdee, 2003. For a map of bottom topography, see Piyakarnchana, 1989, p. 98. The LME consists of three subsystems. A shallow sill limits water exchanges with the South China Sea. For more information on water circulation, see Piyakarnchana, 1989. Salinity in this LME is diluted by rain and freshwater runoff. Monsoons, tidal currents and precipitation impact water circulation, salinity and turbidity. Surface currents run clockwise during the southwest monsoon and counterclockwise during the northeast monsoon. There are seasonal variations in terms of nutrient content and amount of dissolved oxygen in the inner gulf. Aspects of the LME’s oceanography and biogeochemical characteristics are discussed in Wyrtki (1961) and Longhurst (1998). The Gulf of Thailand LME is considered a Class I, highly productive (>300 grams of carbon per square meter per year) ecosystem based on SeaWiFS global primary productivity estimates. Its high primary production levels are the result of increased nutrient loading from rivers and shrimp farms. Primary production is concentrated in coastal areas between Malaysia and Cambodia, and near Vietnam. See Piyakarnchana, 1989, for his study of yield dynamics as an index of biomass shifts. The study includes data on seawater quality, plankton biomass, finfish catch, and yield of other economically-important marine organisms. Species classified as plankton feeders are increasing. For more information on changes in phytoplankton density, see Piyakarnchana, 1989.

Fish and Fisheries

Species harvested include crabs, lobsters, rays, sharks, and small pelagics (mainly Indian mackerels and anchovies). The pelagic fish are caught by artisanal fishermen operating fixed gear such as bamboo stake traps. They supply local markets. Most important among these are the anchovies used for making the fish sauce called Nam Pla (see Ruddle, 1986, and Pauly, 1996). Fish stocks are overexploited. There are major fluctuations of the total catch: from 1.7 million tons in 1985 (see Piyankanchana, 1999), to 2.1 million tons in 1986-1987, 2.7 million tons in 1988, and 1.8 million tons in 1991. Today, the average catch is 1.1 million tons. For a table of total fish catch from 1962 to 1984, see Piyankanchana, 1989. In the 1960s, the introduction of demersal trawl gear led to the development of a Thai demersal trawl fishery, operating in the shallow waters bordering Thailand’s east and west coasts. The ecological impact of the increase in trawling effort was a strong decline in catch per unit effort between the 1960s and the 1990s (see Eiamsa-Ard and Amornchairojkul, 1997). There was a dramatic decrease of the catch, especially for demersal fish and for crustaceans, from 1967 to 1983. See Piyakarnchana, 1999, for reports on total fish catch, average catching effort, and demersal fishes. Pauly and Chuenpagdee, 2003, have analyzed the effect of rapidly growing fisheries on the abundance and composition of tropical multispecies resources and on the ecosystem. For more on the development of trawl fisheries in this LME, see Pauly and Chuenpagdee, 2003. There is evidence of fishing down the food webs. The catch composition has changed to a mix consisting mostly of small, short-lived species. For changes in fish size, see Piyakarnchana, 1989. Crabs, lobsters, rays, sharks and other large fishes were affected by trawl fisheries. For a table of fisheries status and MSY of some economically important marine species in this LME, see Piyakarnchana, 1999. Overfishing in this LME is impacting the productive capacity of this ecosystem. Fishing down the food webs is fundamentally altering the functioning of the ecosystem. A reduction of fishing effort, especially by bottom trawlers, would replenish these stocks and halt further ecological degradation. For more on multispecies and ecosystem analysis, see Pauly and Chuenpagdee, 2003. For a history of the type of gear used in the area, see Tiews 1965, 1972; and Butcher, 1996. The University of British Columbia Fisheries Center has detailed fish catch statistics for this LME. See the graph of Food and Agricultue Organization (FAO) data in Figure 1.

Pollution and Ecosystem Health

The ecosystem health of this LME is fair. Overfishing is impacting the biomass of this LME, and there are increasing amounts of pollutants. For more information on marine pollution, changes in land use, oxygen depletion, the increase in nitrogenfertilizers and eutrophication, and harmful algal blooms, and for a map of red tides in the eastern part of the Gulf of Thailand in 1994 (page 246), see Piyakarnchana, 1999. The increase in inputs of nitrate, phosphate and silicate is causing harmful algal blooms, red tides, and oxygen depletions. People consuming bad shellfish have had food poisonings and illnesses. For these, and other pollution effects, see Eiamsa-Ard and Amornchairojkul (1997); and Longhurst (1998). Water and environmental quality vary seasonally. Low salinity surface water from July to December is associated with low dissolved oxygen. The intrusion of high salinity water from the South China Sea changes the salinity in the Gulf of Thailand. Water quality is lower than acceptable standards in the inner Gulf region, especially at the mouths of the five major rivers, the popular tourist spots along the coast, and near certain islands. Water quality is deteriorating due to increasing inputs of nutrients such as nitrate, phosphate and silicate. These nutrients come from the increased use of fertilizers in agriculture, the mariculture industry and from household sewage. Many cities have no sewage treatment and discharge directly into LME. For more information on heavy metals, see Piyakarnchana, 1989. Mangrove forests serve as buffer zone between the land and the sea, and provide habitats and nursing grounds for many marine organisms. Large areas of mangrove forests are being destroyed to make way for prawn (shrimp) farming ponds, and industrial, residential and tourist development. The clearing of these mangrove forests is leading to a deterioration of the coastal zone and altering the ecological balance of the LME. For more on the wastes released from shrimp ponds, and for tables on the use of mangrove forest land in Thailand, see Piyakarnchana, 1999. For the Thai government’s efforts to protect mangrove forests, see under “Governance”. Oil contamination has been reported, but the oil spills occurring in the LME have caused no serious damage, including the 1992 oil spill near Bangkok Port.

Socioeconomics

Coastalpopulations have utilized this LME for a long time, but in the past these populations were small, and they fished without efficient equipment. In 1959 a new kind of fishing gear, the otterboard trawler, was introduced (see Piyakarnchana, 1989). The catch suddenly increased. Thailand became the major fish exporting country of Southeast Asia (see Floyd, 1984). For more information on fisheries as an economic activity for the local population, see Pauly and Chuenpagdee, 2003. The early trawl operators had extremely high rates of profit, and were moreover able to obtain relatively cheap loans from the Manila-based Asian Development Bank, which helped reduce the cost of entry into the fishery (see Mannan 1997). A detailed economic analysis of the demersal trawl fishery in this LME is provided in Panayotou and Jetanavanich (1987). The study examines various ‘market failures’ (see Sumaila, 1999), and the effect of increased fuel prices in 1973. This increase, along with the EEZ declarations of neighboring countries, gradually forced the return into the Gulf of Thailand LME of a large numbers of trawlers that had been operating outside (see Butcher 1999). For more information on small artisanal fishermen, an important sector of the population when considering environmental impacts, see Piumsomboon, 1994. For a table of the percentage of small scale fisheries production in the Gulf of Thailand from 1977 to 1988, see Piyakarnchana, 1999. Fisheries-related economic activities include the traditional Nam-Pla factories, and the Thai aquaculture industry. Some of the cleared mangrove forests are used for shrimp ponds. The shrimp farmers are presently receiving larger profits from shrimp production than from the traditional uses of mangrove forests. 27% of Thailand remains forested, but this is down from 53% in 1961 (see Piyakarnchana, 1999). The shrimp ponds have polluting effects (see Piyakarnchana, 1989). Tourism and tin mining are other economic activities.

Governance

Carefully constructed fishing regimes and management methodologies could result in increased catches (see Pauly and Christensen, 1993). The Intergovernmental Oceanographic Commission sponsors The Gulf of Thailand website, which contains information about a program for sustainable management in this LME. In the 1990s, the Thai government amended several key environmental laws in an effort to improve environmental quality and protect mangrove forests bordering the LME, and to integrate concepts of sustainable use and development. There was a move towards greater enforcement of conservation laws in the area of fisheries acts and wildlife conservation. The fisheries issue is of the greatest importance. The Thai government is building artificial reefs, limiting fishing zones for bottom trawlers to 3 kilometers from the coastline, controlling catching periods for certain species and controlling the use of certain fishing gears during spawning periods (see Piyakarnchana, 1989). There is an effort to introduce the ‘fishing right’ concept to the artisanal fishing community (see Piumsomboon, 1994). Politically, while Thailand is the major country bordering this LME, Cambodia, Malaysia and Vietnam have historically profited from the Gulf of Thailand LME's wealth of living and mineral resources. A number of conflicts arose in the early 1980's over the catching of migratory fish. Some species of fish are being harvested well before they enter the reproductive stage of their life cycle, which results in economic loss for Thailand.

References

Articles and LME Volumes:

Pauly, D. and Ratana Chuenpagdee, 2003. "Development of Fisheries in the Gulf of Thailand Large Marine Ecosystem: Analysis of an Unplanned Experiment." In: G. Hempel and K. Sherman (eds.). Large Marine Ecosystems of the World: trends in exploration, protection and research. ISBN: 0444510273.

Pauly, D. and Villy Christensen, 1993. "Stratified Models of Large Marine Ecosystems: A General Approach and an Application to the South China Sea," in Kenneth Sherman, et al. (eds.) Large Marine Ecosystems: Stress, Mitigation, and Sustainability (Washington, D.C.: American Association for the Advancement of Sciecne) pp. 148 -174. ISBN: 087168506X.

Butcher, J.G., 1999. Why do Thai trawlers get into so much trouble? MS, presented at a Symposium on “The Indian Ocean: Past, Present and Future”, Western Australian Maritime Museum, Freemantle, Western Australia, Nov. 1999. 18 p.

Piumsomboon, S., 1994. Social possibility and economical aspect of introducing fishing right for the purpose of coastal fisheries management in Thailand. Thai Fisheries Gazette 17(2): 161-168.

Pope, J.A. 1979. Stock assessment in multispecies fisheries. South China Sea Fisheries, with special reference to the trawl fishery in the Gulf of Thailand. South China Sea Development and Coordinating Programme. SCS/DEV/79/19. Manila, 109 p.

South China Sea Programme, 1978. Report of the workshop on management of resources in the Sunda Shelf, Malacca Strait and related areas. South China Seas Fisheries Development and Coordinating Programme. SCS/GEN/78/18, Manila.

Tiews, K. 1965. Bottom fish resources investigations in the Gulf of Thailand and an outlook on further possibilities to develop the marine fisheries of South East Asia. Archiv. FischWiss. 16(1): 67-108.

Wyrtki, K. 1961. Dynamics of the demersal fish resources in the Sunda Shelf area of the South China Sea. Ph.D. diss., University of Washington, Seattle.

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This article is taken wholly from, or contains information that was originally published by, the National Oceanic and Atmospheric Administration (NOAA). Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the National Oceanic and Atmospheric Administration (NOAA) should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Glossary

Citation

(2008). Gulf of Thailand large marine ecosystem. Retrieved from http://www.eoearth.org/view/article/153205